“It was a little like going back to something that wasn’t necessarily going to be particularly challenging,” the 73-year-old actor told THR during a break in filming. “Gandalf is still inside me, as it were, so the business of getting to know a new character -- I was sort of going to be robbed of that.”

And as with The Lord of the Rings trilogy, there was going to be a years-long commitment during which the actor would be working in New Zealand a lot, far from his home in England. (Though breaks have been built in, the commitment has turned out to be longer than anticipated: originally conceived as two movies, The Hobbit is now also a trilogy. Having started filming in March 2011, shooting on the third installment won't be completed until sometime after June 2013.) But a friend asked McKellen how he could explain himself to fans if he quit the project. “You felt, how many millions of people are waiting for it?” he says. “They wouldn’t understand if you weren’t as keen as they were.”

So McKellen says he decided, at the last minute, to sign on. At least this time he doesn’t have to be the very serious Gandalf the White. “Peter Jackson and I much prefer Gandalf the Grey, who was a man who did manage to enjoy himself,” McKellen says. In fact, McKellen seems to be the impish one on the set, clowning and mugging between takes. But he knows it’s important to take the quest seriously. “I was joking around and one of the other actors said, `Stop it, Ian,’ " McKellen says. "And he was quite right.”